Characterization of the electroretinographic scotopic B-wave amplitude in diabetic and normal subjects

The intensity-response function of the scotopic b-wave of the electroretinogram may be a useful device for monitoring patients with retinal disease. Three models were evaluated that describe this function in 152 patients with diabetic retinopathy of varying severity and in 40 nondiabetic comparison subjects. The models considered were the Naka-Rushton equation fit to all 21 data points collected, the Naka-Rushton equation fit to the data points below the "second limb" of the function, and a log-linear fit only to data at the nine lowest intensities. In addition, the b-wave amplitude at each intensity tested was evaluated individually. Model parameters and amplitude measurements were compared with respect to (1) their ability to distinguish diabetic from nondiabetic subjects determined from the area under the receiver operating characteristic curve and (2) their correlation with retinopathic severity, graded in a standard fashion in fundus photographs. When all the parameters of each model were used in combination, there were no significant differences among the models with either evaluation criterion. Furthermore, b-wave amplitudes at midrange intensities (near -2.2 log cd-sec/m2) did approximately as well as any model.